Callum Roberts is professor of marine conservation at the University of York; he was also consultant to the BBC Blue Planet series, and The End of the Line, the documentary based on Charles Clover’s book which deftly exposed the catastrophic reduction in fish stocks around the world. Now, in his monumental new book, he takes a synoptic survey of the global state of the oceans – and does not find much to be cheerful about.

The facts emerge in relentless and depressing sequence. In just a generation many species of fish have been reduced by an astonishing 99 per cent. Whales, dolphins, rays, sharks and turtles have declined by 75 per cent. One quarter of coral reefs have been bleached; in the Indian Ocean, the loss is up to 90 per cent. Rightly, Roberts notes that if three-quarters of our forests had suddenly withered and died, there’d be outrage. As it is, no one seems to care.

Part of the problem is that the sea is so vast and its surface conceals what is going on below. We fly or sail over it, unconscious of our effect on it. Roberts talks of a millimetre-thin membrane that constitutes what Herman Melville called “the ocean’s skin” – in fact the area which concentrates its tiny plants, eggs and other particulates. Yet it is also the repository for all the pollutants we have pumped into the water, and which, when the wind picks up, can turn into an aerosol effect and re-pollute the air of coastal settlements.

Often in Roberts’s book – as meticulously grounded in contemporary science as it is – there is a sense of the sea biting back. The oceans are rising. Warmer water physically takes up more room. Melting ice caps pump water into oceans brimmed to bursting. The Thames floodgates that defend London from disaster were built in 1984. In their first three years they only shut once a year. They now close more than 20 times a year.

It’s a salutary reminder of what the future may hold for the world’s megacities, places such as London, New York, Tokyo, Mumbai, Los Angeles, Buenos Aires and Istanbul. Ten per cent of the world’s population lives less than 10 metres above sea level. The 2004 tsunami in south-east Asia and the 2011 disaster in Japan show that our coasts were once better able to absorb such shocks. Contemporary environmentalists propose that the natural defences of estuaries and mangrove swamps can ameliorate these effects.

The sea is essential to life itself – after all, it produces 50 per cent of the oxygen we breathe. It has sustained human civilisation since our species began. Indeed, as someone addicted to wild swimming, I was fascinated by Roberts’s resurrection of the “aquatic ape” – a contentious theory which posits the notion that early humans actually developed by and in the water. He cites the fact that we have 10 times more subcutaneous fat than any other primate, more akin to that of whales – which, along with our broad shoulders and near-webbed fingers and feet, might indicate an evolutionary disposition to swimming and diving. The theory would also explain the development of our brains, due to a diet of shellfish rich in omega 3 fatty acids.

Roberts hypothesises that the same diet may have supplied cetaceans with their own highly developed brains – now at risk from the product of ours. Their society of sound has been reduced to a bedlam of anthropogenic noise. The perpetual din created by container ships and jet skis alike means that whales and dolphins that communicate in sound now have to shout to make themselves heard. Meanwhile, those shipping lanes constitute an even more direct danger: 50 per cent of all humpback whales in Cape Cod Bay show the telltale white scars of ship strikes and entanglement in fishing gear.

Roberts is determined to end his book on a positive note, providing positive solutions. Those problems are so disparate – and yet, ironically, so interlinked – that the reader is left with an overwhelming impression of oceanic apocalypse. But there is hope in the shape of Marine Protection Areas or MPAs, which have been enormously successful in places such as Lyme Bay in Devon and Lundy Island in the Bristol Channel. We eat sustainably caught fish. We might even stoop to picking up plastic rubbish from our local beaches. Yet all these individual efforts require grander gestures on behalf of governments around the world if they are to make any real difference to the looming disaster.